Hi all,
In this awkward ICE we have a *load_multiple pattern that is being transformed in reload from:
(insn 55 67 151 3 (parallel [
(set (reg:SI 0 r0)
(mem/u/c:SI (reg/f:SI 147) [2 c+0 S4 A32]))
(set (reg:SI 158 [ c+4 ])
(mem/u/c:SI (plus:SI (reg/f:SI 147)
(const_int 4 [0x4])) [2 c+4 S4 A32]))
]) arm-crash.c:25 393 {*load_multiple}
(expr_list:REG_UNUSED (reg:SI 0 r0)
(nil)))
into the invalid:
(insn 55 67 70 3 (parallel [
(set (reg:SI 0 r0)
(mem/u/c:SI (reg/f:SI 5 r5 [147]) [2 c+0 S4 A32]))
(set (mem/c:SI (plus:SI (reg/f:SI 102 sfp)
(const_int -4 [0xfffffffffffffffc])) [4 %sfp+-12 S4 A32])
(mem/u/c:SI (plus:SI (reg/f:SI 5 r5 [147])
(const_int 4 [0x4])) [2 c+4 S4 A32]))
]) arm-crash.c:25 393 {*load_multiple}
(nil))
The operands of *load_multiple are not validated through constraints like LRA is used to, but rather through
a match_parallel predicate which ends up calling ldm_stm_operation_p to validate the multiple sets.
But this means that LRA cannot reason about the constraints properly.
This two-regiseter load should not have used *load_multiple anyway, it should have used *ldm2_ from ldmstm.md
and indeed it did until the loop2_invariant pass which copied the ldm2_ pattern:
(insn 27 23 28 4 (parallel [
(set (reg:SI 0 r0)
(mem/u/c:SI (reg/f:SI 147) [2 c+0 S4 A32]))
(set (reg:SI 1 r1)
(mem/u/c:SI (plus:SI (reg/f:SI 147)
(const_int 4 [0x4])) [2 c+4 S4 A32]))
]) "ldm.c":25 385 {*ldm2_}
(nil))
into:
(insn 55 19 67 3 (parallel [
(set (reg:SI 0 r0)
(mem/u/c:SI (reg/f:SI 147) [2 c+0 S4 A32]))
(set (reg:SI 158)
(mem/u/c:SI (plus:SI (reg/f:SI 147)
(const_int 4 [0x4])) [2 c+4 S4 A32]))
]) "ldm.c":25 404 {*load_multiple}
(expr_list:REG_UNUSED (reg:SI 0 r0)
(nil)))
Note that it now got recognised as load_multiple because the second register is not a hard register but the pseudo 158.
In any case, the solution suggested in the PR (and I agree with it) is to restrict *load_multiple to after reload.
The similar pattern *load_multiple_with_writeback also has a similar condition and the comment above *load_multiple says that
it's used to generate epilogues, which is done after reload anyway. For pre-reload load-multiples the patterns in ldmstm.md
should do just fine.
Bootstrapped and tested on arm-none-linux-gnueabihf.
Ok for trunk?
Thanks,
Kyrill
2016-11-30 Kyrylo Tkachov <kyrylo.tkachov@arm.com>
PR target/71436
* config/arm/arm.md (*load_multiple): Add reload_completed to
matching condition.
2016-11-30 Kyrylo Tkachov <kyrylo.tkachov@arm.com>
PR target/71436
* gcc.c-torture/compile/pr71436.c: New test.